What does this part do?

[Condi]

What does this backing plate (skilfully highlighted) behind the wheel hub actually do? Its thin metal, not supporting anything, and I can only assume is there to divert water away from the brake disk? Is it important if its breaks and is not replaced?

[anarki]

Condi said:

What does this backing plate (skilfully highlighted) behind the wheel hub actually do? Its thin metal, not supporting anything, and I can only assume is there to divert water away from the brake disk? Is it important if its breaks and is not replaced?

It's a brake disc dust shield

[Krikkit]

It shields the rubber components in the suspension arms joining the hub from the heat of the disk, it also catches the dust as well, but that's a secondary benefit.

[Old Merc]

You have almost answered your own question. Yes its a water shield,but its also a heat shield, keeps the heat of the disc away from ball joints etc.
You will find one of those on almost every car. Manufacturers fit for a reason,so if one is damaged replace it.

[hutchst]

You only need it if you want the car to stop when you put your foot on the brake pedal.

[SkodaIan]

When the car is about 4 years old, they fall off when you're driving along, make a horrendous noise and a right mess of the inside of an otherwise as-new alloy wheel.

Then, because of manufacturers being too tight to include a spare wheel and tool kit these days, they cause a long wait at the side of the road for the friendly breakdown man to turn up to take the wheel off to get it out.

Which reminds me, I must get my wife's car booked into the garage to get a replacement fitted....

[lyonspride]

They server a purpose (as someone mentioned above), but I bloody hate the things, it seems like there is not a mechanic alive who can manage to avoid headbutting them hard enough for them to end up grinding against the brake disk.

[tannhauser]

They're there to protect the braking system, surely? Annoyingly on BMWs, they are essential for mounting the handbrake shoes and therefore cannot be omitted.

A PITA to fit too, usually involving rusty bolts and removal of hub, unless you cut sections out...

[Condi]

SkodaIan said:

Which reminds me, I must get my wife's car booked into the garage to get a replacement fitted....

I've got my car booked in to have it removed.

Or at least the offending part which has broken.